The invention relates to a deep hydroprocessing process and, more particularly, to a process for advantageously removing substantial amounts of contaminant such as sulfur from hydrocarbon feedstocks.
A persistent problem in the art of petroleum refining is to reach acceptably low levels of sulfur content and other contaminants.
A large portion of the world""s hydrocarbon reserves contain sulfur, and removal of this sulfur is critical in order to provide acceptable fuels.
Government agencies are currently formulating new regulations which will require sulfur content in fuels to be substantially lower than current practice. It is expected that such regulations will require sulfur content of less than 15 wppm.
A number of processes have been attempted for use in removing sulfur, one of which is hydrodesulfurization, wherein a hydrogen flow is exposed to the feedstock in the presence of a suitable catalyst so that sulfur compounds react to produce a volatile product, hydrogen sulfide.
Such processes do provide substantial reduction in sulfur in the feed. However, existing facilities do not readily provide for reduction of sulfur content to desired levels. Known hydrodesulfurization methods include cocurrent processes, wherein hydrogen and hydrocarbon feed are fed through a reactor or zone in the same direction, and countercurrent processes wherein hydrocarbon is fed in one direction and gas is fed in the other direction.
Known cocurrent processes do not provide acceptable levels of sulfur removal, and countercurrent processes typically experience difficulty in reactor flooding which occurs when the desired amount of gas flow to the reactor prevents flow of the hydrocarbon in the counter direction. Reduction of gas flow to address flooding reduces the effectiveness of countercurrent hydrodesulfurization processes.
Another potential problem with countercurrent processes is that adiabatic countercurrent processes may operate at temperatures much higher than adiabatic cocurrent processes, and this temperature is detrimental to hydrodesulfurization and other catalysts used in the process.
Based upon the foregoing, it is clear that the need remains for an advantageous process for removal of sulfur to levels which will meet the expected regulations on hydrocarbons for use as fuel.
It is therefore the primary object of the present invention to provide a process whereby sulfur content is advantageously reduced to less than or equal to about 10 wppm.
It is a further object of the present invention to provide a process which can be carried out without substantially increasing the equipment size and space occupied by same in current hydrodesulfurization systems.
It is still another object of the present invention to provide a hydrodesulfurization system which accomplishes the aforesaid objectives.
Other objects and advantages of the present invention will appear hereinbelow.
In accordance with the present invention, the foregoing objects and advantages have been readily attained.
In accordance with the invention, a process for removing sulfur from a hydrocarbon feedstock is provided, which process comprises the steps of providing a hydrocarbon feed having an initial characteristic; providing a first hydrogen containing gas; feeding said hydrocarbon feed and said first hydrogen gas cocurrently to a first hydroprocessing zone so as to provide a first hydrocarbon product; providing a plurality of additional hydroprocessing zones including a final zone and an upstream zone; feeding said first hydrocarbon product cocurrently with a recycled gas to said upstream zone so as to provide an intermediate hydrocarbon product; and feeding said intermediate hydrocarbon product cocurrently with a second hydrogen-containing gas to said final zone so as to provide a final hydrocarbon product having a final characteristic which is improved as compared to said initial characteristic.
Still further according to the invention, a system is provided for removing sulfur from a hydrocarbon feed, which system comprises a first hydroprocessing zone containing a hydroprocessing catalyst and having an inlet for cocurrently receiving a hydrocarbon feed and a first hydrogen-containing gas phase; a plurality of additional hydroprocessing zones each containing a hydroprocessing catalyst and including a final zone and an upstream zone, said upstream zone having an inlet for cocurrently receiving a hydrocarbon product from said first hydroprocessing zone and a recycled hydrogen-containing gas phase, said final zone having an inlet for cocurrently receiving a hydrocarbon product from said upstream hydroprocessing zone cocurrently with a second hydrogen-containing gas phase; and a separator for receiving a product from said final hydroprocessing zone and for separating said product into a hydrocarbon phase and said recycled hydrogen-containing gas phase.
The process and system of the present invention are particularly well suited for use in treating Diesel, gasoil and other distillate feedstocks to reduce sulfur and also for use in treating naphtha and like feedstocks as well.